package _1_初级._1_1_数组;

import com.alibaba.fastjson.JSON;

import java.util.HashMap;
import java.util.Map;

public class _1_两数之和 {

    /**
     * 给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
     *
     * 你可以假设每种输入只会对应一个答案。但是，数组中同一个元素不能使用两遍。
     *
     * 示例:
     *
     * 给定 nums = [2, 7, 11, 15], target = 9
     *
     * 因为 nums[0] + nums[1] = 2 + 7 = 9
     * 所以返回 [0, 1]
     *
     *
     *
     */

    //方法一
    public static int[] twoSum(int[] nums, int target){

        int length = nums.length;

        for(int i = 0; i < length; i++){
            for(int j = i + 1; j < length; j++){
                if(target == nums[i] + nums[j]){
                    return new int[]{i,j};
                }
            }
        }

        throw new IllegalArgumentException("No two sum solution");
    }

    /**
     * 方法二：两遍哈希表
     * 出处：https://leetcode-cn.com/problems/two-sum/solution/liang-shu-zhi-he-by-leetcode-2/
     */
    public int[] twoSum2(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            map.put(nums[i], i);
        }
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            if (map.containsKey(complement) && map.get(complement) != i) {
                return new int[] { i, map.get(complement) };
            }
        }
        throw new IllegalArgumentException("No two sum solution");
    }

    /**
     * 方法三：一遍哈希表
     */
    public int[] twoSum3(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            if (map.containsKey(complement)) {
                return new int[] { map.get(complement), i };
            }
            map.put(nums[i], i);
        }
        throw new IllegalArgumentException("No two sum solution");
    }

    public static void main(String[] args) {
        int[] nums = {2,7,11,15};
        int target = 9;
        int[] result;
        result = twoSum(nums, target);
        System.out.println(JSON.toJSONString(result));
    }


}
